The present invention relates to a run-flat low-pressure tire for all terrain vehicles (ATV) wherein the tire has a unique tread, sidewall structure and bead which permits the tire to be run even if the air is released by a puncture or the like. The inventive tire can be designed to provide limited run-flat capability or alternatively can be designed to operate nonpneumatically without any internal air pressure.
ATV tires are designed to work in assisting cooperation with the vehicles suspension system. Accordingly, the tires are wide and relatively tall in comparison to the nominal rim diameters which generally range from 8.0 inches to 12.00. These tires exhibit large air chambers which are held at pressures generally below 10 psi often about 2.9 psi and have relatively compliant sidewall structures which in combination with the vehicle suspension act as shock absorbing and vibration dampening components of the vehicle.
These vehicles operate in very rugged terrain and due in part to the low operating inflation pressures the ATV tires mounted on its conventional rim has been subject to becoming unseated in sharp cornering maneuvers. Even more problematic has been the tendency to have the beads unseat during an uninflated condition such as a tire puncture.
Eiji Nakaski of Sumitomo Rubber Industries recognized this concern and invented run-flat tires and rim assemblies for ATV vehicles. These tires described in U.S. Pat Nos. 4,940,069 and 5,186,772 have a protrusion radially and axially inward of the bead. The protrusion is adapted to fit over a hump in the rim and engage a depression or groove in the rim axially inward of the hump. The resultant fitment is said to enable the tire beads to stay on the special rim without the assistance of air inflation during normal operation.
Besides the obvious need to employ a special rim when using the prior art tire of Nakaski, the tire itself was prone to damage both on assembly but most particularly upon removal and repair. The protrusion could be easily torn and damaged and once damaged the tire was useless as a run-flat tire. Furthermore, the purposed range under run-flat conditions was 100 km.
The present invention discloses a novel bead design which enables run-flat functionality to be achieved with the use of the conventional 5.degree. taper ATV rim.
The use of conventional rims with run-flat automobile tires was first commercially successful in the early 1990's when it was disclosed in U.S. Pat. No. 5,368,082, issued on Nov. 29, 1994, in the name of Thomas Oare, et al. This automobile run-flat tire employed a unique bead configuration and a very low aspect ratio carcass to achieve the desired run-flat results. Due to the short section height and relatively high weight load requirements the deflection of the tire under load was greatly limited. The present invention has uniquely different design constraints in that the aspect ratio of the ATV tires are generally 50% to 100% yielding a very tall sidewall section height (SH) that must also be sufficiently compliant to deflect about an inch acting as a shock absorbing assist to the comparatively primitive vehicle suspension of the ATV vehicle. The maximum load per ATV wheel position is lower than an automobile, generally less than 500 lbs/tire whereas the above-referenced automobile tire had a minimum load condition of approximately greater than 1,000 lbs. To better appreciate these differences an automobile suspension spring rate is about 200 lbs/in. Its associated auto run-flat tire will have a spring rate of 1,000 lbs./in. The ATV vehicle suspension struts have a spring rate of 80-100 lbs./in. Where as its associated run-flat tire has a spring rate of 160 lbs./in. to 200 lbs./in. In the ATV tire if the run-flat tire's spring rate is too high when the tire is operated inflated or noninflated, the rider will find the ride extremely harsh and difficult to control The present invention contemplates these unique ATV design constraints and teaches a novel tire structure which has excellent run-flat characteristics while maintaining the soft compliant ATV tire features without requiring a special rim.